RADV Vulkan Driver Patch For Initial PRIME Support

David Airlie's latest hacking on the RADV open-source Radeon Vulkan driver code has led to basic PRIME support for this unofficial driver.

RADV users on a multi-GPU system can now have working rendering when the DRI_PRIME=1 environment variable is set. Dave explained with the patch:

This is kind of a gross hacks, but vulkan doesn't specify anything but it would be nice to let people with prime systems at least see some stuff rendering for now.

This creates a linear shadow image in GART that gets blitted to at the image transition.

Now ideally: this would use SDMA - but we want to use SDMA for transfer queues maybe we don't expose a transfer queue on prime cards who knows.

we wouldn't have to add two pointers to every image, but my other attempts at this were ugly.

Is the image transition the proper place to hack this in? not really sure anywhere else is appropriate.

It also relies on DRI_PRIME=1 being set, I should be able to work this out somehow automatically I think, probably getting a DRI3 fd from the X server and doing drmGetDevice on it, and comparing where we end up.

It's not yet in Mesa Git, but presumably will be there soon enough given the recent pace of RADV development.